JPH0281432A - Method of forming phosphorus-doped polycrystalline silicon film - Google Patents

Abstract

PURPOSE:To obtain a uniform phosphorus distribution in a low concentration region among wafers by a method wherein monosilane and trimethoxy phosphoric acid are employed and a phosphorus-doped polycrystalline silicon film is formed in a specific temperature range. CONSTITUTION:In monosilane (SiH4) and trimethoxy phosphoric acid (PO(OCH3)3) are employed and a forming temperature is selected within a temperature range of 550-700 deg.C, PO(OCH3)3 is not decomposed in the gas introducing side of a reaction chamber and has a high resistivity and is decomposed in a wafer region by heat and is gradually taken into a polycrystalline silicon film. By selecting the suitable forming temperature, therefore, a uniform phosphorus concentration distribution can be obtained. In a low pressure CVD method, SiH4 and, instead of PH3 which has a high adsorption speed, trimethoxy phosphoric acid PO(OCH3)3 are employed as raw gases.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing a phosphorus-doped polysilicon film used as a wiring material for LSI devices.

[Conventional technology]

Conventionally, when a polysilicon film is used as a wiring material, its production is performed by the following method.

The first method is to implant ions such as P and As into the polysilicon film, and the second method is to implant POC1 into the polysilicon film.
3, etc., and the third method is Si
This is a method of producing a phosphorus-doped polysilicon film by thermal CVD using H4 and Plh.

With the first ion implantation method, it is difficult to implant ions into parts with deep steps, and with the second diffusion method, it is difficult to control the phosphorus concentration and obtain concentration uniformity. Direct generation methods using methods are attracting attention.

[Problem to be solved by the invention]

However, the method for producing phosphorus-doped polysilicon films using SiH4 and PHff requires hot-wall thermal CVD.
In order to obtain uniformity of phosphorus concentration in a large number of wafer regions in the apparatus, it is necessary to add an excessive amount of PH.

Figure 2 (a) shows the generation rate and PH3 with respect to the wafer position.
This is a diagram showing the relationship between the flow rates of PH3 and 200.
cc/win, b line is the same < 150cc/mi
The n and c lines are the same < 100 cc/min, and the a line is the same (showing the case of 50 cc/min. Also, Figure 2 (bl is a diagram showing the relationship between resistivity and PH5 flow rate with respect to wafer position, and a The line shows the flow rate of PH1 is 200cc
/min, b line 150cc/min, c line 100cc/ffl1n, d line 50cc/min
The case is shown below. Both are 50χSiH4/, 450cc/min, 0.5! PH38. 50~2
00cc/min, pressure 50pa, temperature 620℃
The figure shows the case measured under the following conditions. This figure 2 (al
, PR as seen from (b).

need to be used in large quantities.

In addition, as shown in the third figure, height H=4.2μm9 width W-2,
When a phosphorus-doped polysilicon film is formed on a 6 μm concave step portion at a temperature of 615° C., the step coverage of the film at the step portion, that is, the film thickness dimensions A, B, and C at each part is P)lz/ When the ratio of SiH4 (phosphorus concentration) is changed, as shown in the table below, there is a problem that the lower the phosphorus concentration is, the better it is, and the higher it is, the worse it is.

[Means to solve the problem]

In order to solve the above-mentioned problems, the method of the present invention uses monosilane and This method is characterized in that a phosphorus-doped polysilicon film is produced using trimethoxyphosphoric acid in a temperature range of 550° C. to 700° C.

[For production]

In this way, using monosilane (Silla) and trimethoxyphosphoric acid (PO(OCH3) 3), the generation temperature was set to 55
When selected within the temperature range of 0℃ to 700℃, PO(O
CH3)+ is not decomposed on the gas introduction side of the reactor, has a high resistivity, is thermally decomposed in the wafer region, and is gradually incorporated into the polysilicon film. Therefore, by selecting an appropriate generation temperature, a uniform phosphorus concentration distribution can be obtained.

〔Example〕

Embodiments of the method of the present invention will be described below with reference to the drawings.

When SiH and PH are used as source gases, Pt
The rate of adsorption of h onto the Si wafer surface is fast, as shown in Figure 4, and reaches its maximum (peak) at 550°C to 650°C, which is the temperature at which a normal phosphorus-doped polysilicon film is formed. In this case, 51g4 is SiHn (g) - 5iHz (g)
A reaction at 10 Hz (g) generates 5 iHz, and a reaction with PH3 generates 5i) 12+PII:+→SiH, PHz, forming phosphorus-doped polysilicon. For this reason, P
The rapid adsorption of phosphorus is not desirable in order to obtain uniformity of the phosphorus concentration within and between wafers.

In the method of the present invention, S is used as the raw material gas in the low pressure CVD method.
i It =, and triquimexylic acid PO(OCH3)3 is used instead of PH3, which adsorbs quickly.

PO(OCH3):l is a liquid raw material with a boiling point of 197°C, and its adsorption onto the Si wafer is not as obvious as with PH.

When changing the formation temperature and observing the variation in resistivity between wafers, we found that Pll3 has a low resistivity on the gas introduction side, as shown in Figure 1a, while PO(OCH
3) 3 is not immediately decomposed on the gas introduction side, has a high resistivity, is thermally decomposed in the wafer region, and is gradually incorporated into the polysilicon film. In Figure 1, b shows the generation temperature at 600°C1. Similarly, c shows 620°C. Similarly, d shows 640°C.
It shows the resistivity versus wafer position (area) in °C.

Therefore, by selecting an appropriate generation temperature, a uniform phosphorus concentration distribution can be obtained.

〔Effect of the invention〕

As described above, according to the present invention, when forming a phosphorus-doped polysilicon film by thermal CVD, PO (which is an organic raw material) is used instead of Plh, which is quickly adsorbed to a silicon wafer.
By using OCH3)3, it is possible to obtain uniformity of the phosphorus concentration distribution between wafers in the low concentration region.

[Brief explanation of the drawing]

Figure 1 shows the conventional PH and the PO (OCIh) of the present invention:
Figure 2(a) shows the relationship between the generation rate and the flow rate of PH3 with respect to the wafer position.
b) is a diagram showing the relationship between the resistivity and the flow rate of PH3 with respect to the wafer position, and Figure 3 is a diagram showing the step coverage of the film in the step part when a phosphorus-doped polysilicon film is formed at a temperature of 615°C in the step part. , FIG. 4 is a diagram showing the relationship between the generation temperature and the rate of adsorption of PH3 onto a silicon wafer when a conventional PHff is used. Note Z so-called (a) '10 to 0 generation rate (A/)

Claims (1)

[Claims] In the low-pressure CVD method, which generates a phosphorous-doped polysilicon film on the wafers by heating a large number of wafers carried into a reactor while flowing raw material gas, monosilane and trimethoxyphosphoric acid are used to heat the wafers at temperatures ranging from 550 to 700 degrees Celsius. A method for producing a phosphorus-doped polysilicon film, the method comprising producing a phosphorus-doped polysilicon film in a temperature range of .